The present invention relates to a load cell and more particularly to a variable reluctance load cell which is sensitive to relative displacement along a preselected axis but is relatively insensitive to displacements along transverse axes and to bending moments.
It has previously been proposed to use variable reluctance transducers for force measurement. For example, U.S. Pat. No. 3,206,971 to E. Felix discloses the use of a core and winding for sensing changes in proximity to a cantilevered spring. Changes in the inductance caused by changes in the gap between the core and the spring are then reflected in the frequency of an oscillator circuit which employs the inductance as a frequency determining component. Transducers of this type, however, have apparently never enjoyed any great popularity. This is believed to be due to inherent non-linearities in previous designs and due also to sensitivity to forces along axes other than the one intended to be measured. A somewhat analogous field of prior art is that of linear variable differential transformers (LVDTs) which are commonly used for displacement measurement and provide outputs whose amplitudes vary as a function of the measured displacements.
Among the several objects of the present invention may be noted the provision of a load cell utilizing a novel variable reluctance transducer; the provision of such a load cell which responds principally to forces along a preselected axis; the provision of such a load cell which is relatively insensitive to forces along axes transverse to the preselected axis; the provision of such a load cell which is relatively insensitive to bending moments; the provision of such a load cell which provides measurements of high repeatability; the provision of such a load cell which provides measurements of high precision; the provision of such a load cell which is highly reliable and which is of relatively simple and inexpensive construction.